Nikon D6 Reference Manual page 264

D
Mirror Up
•
Photos cannot be framed in the viewfinder.
•
Autofocus and metering are not available.
A
Taking Pictures
•
Use of a tripod is recommended.
•
Press the shutter-release button smoothly to prevent blur.
•
The mirror lowers when shooting ends.
•
A picture will be taken automatically if no operations are performed for
about 30 s after the mirror is raised.
•
In live view, the picture is taken the first time the shutter-release button
is pressed all the way down.
212
Choosing the Operation Performed When the Shutter Is Released (Release Mode)